Volume control in telephone circuits



Sept. 26, 1933. s. B. WRIGHT ET AL 1,927,999

VOLUME CONTROL IN TELEPHONE CIRCUITS Filed Deo. lO, 1930 2 Sheets-SheetIl Sept. 26, 1933.

S. B. WRIGHT ET AL VOLUME CONTROL IN TELEPHONE CIRCUITS INVENTORSATTORNEY Patentedvsept. 1.933 Q f I i l UNITED? STATES' "1,927,999,VOLUME ooN'rRoLrN'TELErnoNEQ CIRCUITS j e Sumner B. Wright, SouthOrange', N.- J.,'.`and 'Edmund ILT.' ylor, New York, N.-.Y., as signorsn to American .Telephone `andTelegraph Com-,

pany, a. corporationof Nevvlork.l y .Y 'y

Application December 10, 193i) i' Serial No. 501,414 I This inventionrelates to telephone circuits and desired resultof'irnprovements'inconnection'vvith particularly to two-way telephone circuitsy intransmission circuits of this type isthe prevention which four-wirecircuits are connected :to twoor" false operation of thevvoice-o'perated` devices, Wire lines. More particularly, the inventionrealong with the ability to deliver the greatest pos-ff 5.- lates to thecontrol ,of volume, especially the re` sible andV desirable volume overthereceiving pathvr 6 0 ceived volume, at a terminal of the four-Wire atthe terminal.` Whenanti-singing voice-op--. circuit and to such controlin combination with erateddevices' areemployed'- on vthe circuit', `thecertain other adjustments, as will appear hereinvmaximum Areceivedvolume consistent, with the after. The invention is applicable to wirecircuits. suppression of false operatinof the anti-singing and tocombined Wire'and'radio'circuits,. devices dependsuponthe followingfactors: thei 65 ,l The invention has been made and willibe betterminalbalance,"th`e ability of the' talker toopter described with. more orlessv particular refcrate the voice-controlled relays, the v ratio ofE,the i erence to a transoceanic radio telephone system. Vnoise to thevolume deliveredby thetalker, the It is to be understood, however, that;Athe invention ratio of'static to thereceive'd volume (injthecase 15.15applicable to other telephone systems` differof'alr'adio circuit)v andthe hangover timeofreci'fo ing from a transoceanic radio system as totranslayswhich are fsubject to false i operation by' j mission media andas to-details; for instancait static. f Vv is applicable to submarineAcable` circuits. vThe In connection Withthe .typical'lou r-vvils` Giri,description willhave. particular .reference to the cuit connected at theterminal to-a two-wire line"v r n f four-wire circuit which, in thecaseof, the transwith the usual arrangement ofA hybrid coil and 75.

oceanic radiosystem, lies intermediatefone terminetwork to balance thetwol-wire line, 1ct Sr repnal of thesystem and the radio link; resentthe sensitivity of vthe fanip'lierdetector t will further theunderstanding of the ,inven-l connected acrossthereceiving path ofthefourtion and obviate the necessity of considerableQdewire circuit-(expressed indecibelsL/Lr the lossl y V scription and discussion ifreference is hadito' of the receiving path'volume` control, RL the re-80 the published disCiOsilI'eS 0f the DliOIialt Ilpls.-A turn loss lof.theconnection between the four-'WireA sented -by the following: ArticlebyfClark and circuit and the two-Wire'VVA line, .Lt thev .loss of.Mairies, Journal 0f American-vInstitute of Electhe volume* control inthe transmittingpath.ofv trical Engineers,v June, 1925, pages 618 to626; the `four-wire circuit, .St the sensitivity ofi the"` f 39' UnitedStates Patent N0. 1,607,637 i50xH- Nyquist, amplier-detector connectedacross thetr'ansn'iit- 85j and UnitedStates Patent Ito-1,690,182 to H.C. ting pathand Lkthelalgebraic suml of allthe Silent. L fixed lossesbetweenv the points of connection of Telephone circuits in which areemployed voicethe two amplier-detectors-with thev transmission Operateddevices for the Suppression 0f Singpaths. False operation of.thefhtransmitting f ing and irl Whh the Signal t0 noise .ratio iSvoice-operated devices bya signal returning over` 99; of greatimportance involve certain controls of the two-wire line and.entering'the transmitting` transmission volume and of the sensitivityof branch 4of the four-wire circuit will occur if the voice-operateddevices. The four major .conf trols found necessary at present are thoseof the STLH-ELi- Lts t+1; k Y Y .1. l 40 transmitting volume, thesensitivity of the transis less than zero. rIhe condition AforJfalseopera- 9.5 p.

znittingy voice-operated devices, the sensitivity of tion so's'rtatedhas been realized, and'thefattempt v A the receiving voice-operateddevices and the volhas beenmade to prevent the false .operation by. urnein the receiving path. When a circuit of this manually decreasing thereceived 'volume in the y type terminates, as is usually the case, in atwo-k four-wire circuitwhenever the step ldifferencefof ib wire circuithaving a return loss less than iniinlthe various manual controlshasfexceededa cer- 1-00 ity, there is inevitably present aninterdepend-- tain predetermined amount. lIf proper results ence betweenthese controls, since a wave comare to be' obtained, such adjustmentinvolving f ing in over the receiving path of the circuit whichcomplicated-computation must be'made very rap-l is not strong enough tooperate the receiving reidly, and it is .evident that the demand uponthelays vvill pass into the two-Wire circuit and then `average technicaloperator is excessive.' Conse- 105 pass from the two-Wire circuitintothe transmitquently,.,this1nanua1 adjustment of the received ting path,where it may cause false operationfof vvolume is likelyto'result-,either in anexcessive f the devices vassociated with thisltransmission amount 'of false operation or in the deliveryt'o path,which should be operated only bythe voice the'subscriber ofunnecessarily 10W volume. A Furi signals coming over the two-Wirecircuit.' The tllelmore', the requirementsl of themanual ad- 110".justment have resulted in non-uniform designk of control apparatus,'Withra view to simplifying thev computations; The'problem is furthervcomplicatedY by the relation between the sensitivity of the receivingVvoice-operatedv devices and the hangover time of the receivingrelayswhich may be operated by static inthecase of a radio linkinthe'system.V

The principal object of the present invention as applied tothe type ofVcircuit' undergparticular discussion is theautomatic control'of thereceived v,

volume to prevent false operationof the.trans.V mitting voice-operateddevicesv withoutunnecesksary reductionA of -thatvolumejunder any'- cire''cumstancesf Other objects ofthe invention will be understood from thefollowing statements of various advantages 'which are found'in theA Auseof theinvention: v i YApparatus may be used for ythe 'various con-:trols which is of uniform design, the 'control sets thus beinginterchangeable.

.Should it be .desirablefor any reason to .shift from the automaticVcontrolof Ythe received fvolume, with .which no' computation bythe'operator isrequired in ordertoadjust that volume, `to the v'manualvcontrol of the received volume, the circuits can be adaptedto suchshiftby asingle'simyreadily observed .signal ple switching operation. i

In the case of automatic control of the received volume and in the caseof the'manual controLUa is properly adjusted.`

' If the circuit connected tothe four-wire circuit is changed from ashort localr circuit to a long toll line, -suitahle, adjustmentisautomatically made,

of circuit being .taken into'consideration. K

VIf a two-wire circuit'ofwhich `the return loss the 'average return loss'in the case of either typev Y isknownjto Adiffer from the` average isconnected to the four'fwire circuit, suitable adjustment isA justment inconnection with a change in the type readily made.

Any onejor all changedto automatic control without affecting the maincircuit Whichvco'ntrols 'the received volurne. i

i In general, the applicants attain the objects of their'inv'entionvandprovide the various advantages vthereof bycausing the adjustment ofthe transmitting volume,V the vadjustment ofy the. transmittingsensitivity land the adjustment of the 'receiving `sensitivity .toycontrol jointly and automatically the adjustmentof the received volume.-In addition, they provide for suitable adofj connected'circuit, willappear hereinafter.

V 5'; The invention will be clearly'understoodwhen inthertwc figures o"the drawings Y responding circuit elements; A

Vthefollowingdescription is read with reference-to Ythe accompanyingdrawings, in which- 1 Figure lshow's schematicallyl the"application ofthe applicants control methods to the terminal of a two-way'system suchas the transatlantic radio telephone system, and

" Fig. 2 shows diagrammatically and in'considlv era'bledetail onekcircuit arrangementsuit'able to thepractice of thereinvention.` Y l'Inseveral instances, like reference ,characters is given when thecircuit 'of'. the Amanual controls can loeV designate cor-j 'Withreference, rst, to Fig. 1' of the drawings, it is assumed l that thetransmission path L1 is a twowirerpath forming `the branch of afour-wire .circuit adapted for'transmissionv from Westwto east, Yforinstance, that'the .transmission 'path L2 is the two-wire :path formingthe branch of the four-Wire circuit `adapted'ior transmission from eastto west and vtlflat'the two paths L1 and L2 are .connected at their westterminal to a switchboard drop; and an lextension circuit through theusual arrangement 'of a hybrid coil and a network designed to give acompromise balance against number oi different circuits. lt ;isunderstood Vthat the circuit may have connected to,V it a toll' line oiconsiderable length, as is indicated but not fully shown inA thedrawings. .A circuit-conf trolling .relay R1 is schematically shown inthe transmitting line L1,.and a second circuit-convtrollingrelay VR2 islikewise 'shown in the receiving path L2. These tworelays arevcontrolled, by

Van'ampliiiendetector AD1 connected 'across'the f transmitting lineLu'and, as is well .understoodin 'the art,the rela'y R1 is usuallytermed the singing suppressor relay. HA second faniplierrdetector" ADais vconnected across the receiving path La and, as is well understood'in' the art,"has as one of'its functions the control cifarelay R3 inthetransmitting path L1 which may be'terin'odthe false operation suppressonrelay. It is sumcient to' state herein that'relay'lts functions toprevent the operation "ci the amplifier-detector 'AE1 and the relays kR1and Rzw'hen such 7.operation is undesir` ahle'bu't'wo; d' occur duetofconditons in the cirn cuit were i notfor thepre'sence of relayl R3.The apparatus Ysuch as arnpliiiers and delay c' cuitssohematicallyjshown are well understood inthe The, fourcircles includedin the scheme represont manual controls oil the natureV in'dicatedjandYthe solid'lines indicate `the control vloyV these .maneualmeanso'flosses and the like at-certain points the circuit. Itwill' benoted that a s'olid;,line lune from each oiv the four'manual controlsjtoa and subtracting'rnachine. It is to be 'understood thatin thecase offull manual adjustment of the Y circuit the technical operator, uponmalring'any one'of' the manual'-adjustments, makes certain computationsand then adjusts the received vol- Vurne,accordingly. Fig. 1' of thedrawings, yis intended to convey the idea that, in the case of fullmanual control, the net adjustment of the received volume is the resultof thevarious computations and resultant manual adjustments 'ofth'atapparatus which directly controls the received volume.

In addition, itis indicated in 1 that the connection of the fourewirecircuit to a toll line automatically has certain effects which will bemorefully considered hereinafter; j

f 'While the number of transmission units :in--

volved in the volume and sensitivity control is-in itself no part of theinvention, it will clarify thel description if alimited'nuinber ofiiguresiresulting from the operation of the transatlantic radio,telephone circuit are 'used in this discussion.

The receiving volume control takes caredof low range in transmissionunits of'20 decibels (db).

The transmitting volume control functions to Vary the transmittingvolume so that Ta constantS volume will be delivered to the associatedvoiceoperated devices, involves a decrease of received volumewhen theoutgoing speech is weak and requires a range of 45 decibels. Thetransmitting sensitivity control functions to raise the sensitivity ofthe transmitting.'voice-operated devices to Vprevent clipping and tolower the sensitivity to prevent operation by noise, involves a decreaseof vthe received volume when the sensitivity is high and an increasewhen the sensitivity is low and requires a range of 20 decibels. Thereceiving sensitivity control lowers the sensitivity-of the receivingvoice-operated devices to prevent operation by static, involves adecrease of the received volume when the static is high and requires arange of 36 decibels. In addition to these four` major controls there isthe controlY of the hang-- ceiving sensitivity with an increase of thehangover time and requires a range of 10 decibels.

From the above discussion; it is seen that if the various adjustmentswere independent, the

proper control of the circuit would involve a` volurne range of 131decibels. As a matter of fact,

however, it is found that, since the various factors do not applysimultaneously, the actual volurne range which must be considered in thecircuit under particular consideration is about 43 decibels. The variouslosses or adjustment ranges indicated in Fig. l are basedv on theeirperiencewith the transatlantic circuit as dis- The transmittingvolumecontrol operates to adjust the variable loss indicated in thetransmission path Li. Without the use of applicants invention, theoperator in charge of thiscontrol would then make certain computationsand make the suitable adjustment of the received volume.

In accordance-with the applicants method, `the 'adjustment of thevariable loss in the line L1r automatically affects the adding andsubtracting machine and thus contributes to the control of the receivedvolume through adjustment of the variable loss indicated in the.receiving path L2. l

The transmitting sensitivity control adjusts the variable loss indicatedahead of the amplifierdetector AD1 and, with full manual operation, theusual computation would be followed by manual adjustment of the receivedvolume; 'also a certain auxiliary adjustment of the loss in the path L2should be made. `The dotted lines indi- 2 ofthe drawings. i a ,u K5.

In general, suitable automatic controlof the received volume is providedby arrangingpotentiomet'ers at the 'input-ofthe amplifier-detectorsprovides for the proper-contribution tothe add-` cate how the applicantsautomatic"arrangement' ing and' subtracting machine to'take the place ofe i v the transmitting-sensitivity-control` operators computations andmanual adjustment of'the re- A ceiving loss. Y.

The receiving sensitivity control adjusts thezva'- l vriablelossfindicated' at thetinput of 'the amplilier-detector ADE,which'controls the false-'operation suppressor? relay R3. L Theapplicants pro-v vide for automatic adjustment of the received volume'which is suitable in .view of thisfsensi'- tivity adjustment. Y

It remains toconsider u should be .made With-a change :of circuitvconthe adjustmentswhich v nected to the four-wirecrcuit at its west end:"It will be assumed that the `hangover time oi"v the voice-operateddevices controlled by the ampliner-detector vA132, represented by relayR3 vini Fig. l, is suitable for' the case of a' local (circuitconnectedto the .four-wire circuit.' If, howevenf-a: long toll line isconnected;` a` longer hangover f, f

time must be providedfor'therelay Re, for .in-j u stance, especially ifthe toll line isr not Aequippedl with echo Suppressors. The most'suitable'ar-i rangement forr adjusting in accordance with thedifference of connected circuit iappearstobe' the following: i

A 6 decibel pad is AnormallyV connected switchboardcircuit at` rthe westend of the fourwirecircuit, as indicated. V.Iii a toll line isicon-vnected Vto the Afour-wire circuit, battery is automatically connectedtothe'sleeve lead, and the A6 decibel pad is cut outv of thecircuit. iIn .addition, this sleeve connection adjustsa variable" y loss ahead or"the ampliiier-.detector ADz, fhas certainj'direct effects on the relay.R3 and pro'- after in connection with Fig. 2 of` the drawings.

It now proposedto' describe inysomerdetail one circuit arrangementsuitable tothe practice of the applicantsmethod more generally'discussedin connection with Fig. 1.y The following:

description should .be read with reference tov Fig.` d

in thecase of sensitivityy controlor.y at the input maining unchanged.Provision of the two amplifier-detectors and their' associated apparatusare the Vsaine and, as stated above.; `let' Lr represent the loss ofthereceiving-volume control, RLthe return loss ofthetwo-wireconnectio'nyL the loss of thetransmitting'volurnercon-l trol andLk the algebraic sum of` the iixed loss between vthe points of.applicationofgthe Atwo amplier-detectors; "inf addition, 'let L'raarepresent'the loss immediately `ahead ofth'e` receivingampliiier-detector and Luid the loss immediately j ahead of thetransmitting ,"amplier-detector.

We now nd that'theequation representing the vits' condition forfalseoperationoi thesinging-suppressor relay becomes: i l u f YLma-l-'LmgRLjLLLJF-LfadJrLky isless than Zero. VThis is a linearequation,` and.

all'of the terms are losses.' Accordingly, the .u'

applicants use as their `controldevice or adding il K and subtractingmachina al control lcircuit conY sisting of a marginal-,relayarrangement in series withza battery and a pluralityovariableresistancesV which correspondY each to one of the variable :terms vofthe equations; vEach of the variable resist'ances is controlled to'haveVa value which at all times variesin accordancewith they Yvariation fofthe corresponding loss.l The marl* ginal relay arrangement is made toproducean ,indicationVV when the equation is solvedk anda n secondindication if the equation is a prede-J termined distance from beingsolved.

. With referencetothe details of'jFig'. 2, the,k transmissionpaths L1and L2,V the hybrid coil HC and the network for balancing the lineconnected Vto the four-,wirecircuit are as shown in paul- L2.

Fig. l.Y The usual an'iplifiers` and delay circuitsy in the Yfour-wirecircuit are shown or indicated;4

the amplifier-detector AD1 is connected across theV transmission VvpathL1, and thel amplier.- detector A132, is connected across thetransmission Ahead of the line aniplifierin transmitting path L1 isapotentiometer arranged for, manual s control of the transmitting-volumeby theoperation of switch having contacts 0 ment of thejswitch arm toincrease vthe loss introduced.. The closing of any one oirthese contactscompletesa circuit through a certain relay, and

the loss 'through the potentiometer is'thus 'controlled in awell-knownmanner; it will bel noted'rthat to the left of the `poter'itiornetercontrol contacts and armatures there is shown a second 'ceived volume.

setV ofcontacts controlled by the respective relays i toconnect into thecontrol circuit, to be discussed below, a resistance.havingV equal stepsof rSi: ohms each, it being `understood without iurther labeling that`in this case `and other similar cases in Fig. 2 the yresistance sectionshave equal values. `Y

Potentiometers` and the manually-operated `controls therefor, similar tothose just described,

are found in the circuit as follows: one ahead of the transmittingamplier-detectorADi for con# .trollingjthe sensitivity thereof, koneahead ofthe receiving Yanipliierdetector'ADz vto control its`Ysensitivity and one ahead of the line amplier in the receiving branchL2 for` the control of the re.-

It i'srthis last; control, that Vof the received volume, whichapplicants propose to'operate automatically under the joint control ithe V otlnerV three'major adjustments and of VVthe, hangoverv adjustmentto be discussed more for an increase oiloss.

fullyhereinafter. Infthe showing or" the transmitting sensitivitycontrol, the Yarrow indicates the movement ofthe switch arm foradecrease of sensitivity; in the receiving sensitivity control a like.direction of adjustment isY indicated, and in the'case of the receivingvolume control the arrow indicates the movement of the switch arm ItWillfbe understood, of course', that .any suitable number of steps mayvybe introduced to meet the conditions and restated above is ysolved-thatis,l the operation 4of Vthisrelay indicates that without adjustmentfalse Voperation-is to be expected similarly,- the opera .tion of relayRjindicates that vthe equationis incre-'thanv a. predetermined amountfrom being solved and'that thereceiving,volume may be in-V creased;without immediate .dangery of false 'op-Y eration. Associated with therelays YR and R7 are relays R4, RtyRacertain other relays directly.

controlling the receiving loss, and'relays Ra and R9, which have todowith the hangover adjustment and are operatedvalong with a relay R1 inconnection vwith the inclusionin the circuit of a toll line. I

The main control lcircuit which corresponds toV the adding andsubtracting machine of vFig. 1

may be traced Aas follows:l from ground atG through battery, thevright-hand armature of relay R5, the upper'Winding` ci relay R', theupper winding of relay R, through the resistance 'asso` freceiving-sensitivity control;I through resistance r and 1" (to bediscussed here-- ciated Ywith the inafter), through .the resistanceassociated with vthe receiving volume control,l through a switch andresistance `arrangement called the.return through the resistanceassociated with the transvmitting volume control 'and through theresist-'- ance associated with the transmitting vsensitivity control toground at G lIt will be understood logf loss compensator, to bediscussed hereinaiten that the various loss controls, including Vthere-` f ceived volume controL'notronly malte the volumev or sensitivityadjustment ldesired but also' adjust the series reistances in thecontrol circuit. Asilo.

indicated above, the' .proper margins for relays R and R are obtainedfrom thelower orbiasing windings, which are lin series with a resistanceand with 'battery'. ItV should be noted here that if the batteryconnected to these biasing windings is the same the battery of thecontrol circuit shown normally*` connected to the righthand armature ,ofrelay R5, battery fluctuations are rendered negligible. It will beunderstood,- ofcourse, that. theexternal resistance of the. con`` trolcircuit determines whether the `relay R and the relay R are in operatedor unoperated condition. 1t will be noted that signal lamps S1 and Siareconnected in circuits controlled by relays R andR'.. Ifboth relaysare unoperated, the

lamp S1 lights to indicate thatthereceived volunie may be increasedwithoutimmediate danger oi false operationof the voice-operated device.i" bothfrelays are operated, lamp Sailights to indicate that there is'danger' of false operation and that theA received volume should bereduced. The advantages of. these signal lamps will be discussed furtherhereinafter.

The direct control vot the received volume ywill now be described. It isseen that the'switch for the received volumey control with manualI operation rmakes contact` at the point 0 or at-'point l or at point 2V or atpoint '"3. tact is at point 0, the uppermost ofthefour relays operatesv(assuming that ground is connected tothe switch arm) and the right-handarmature of this vrelaycompletes the transmis# sion circuit at the topofthe potentiometerthat is, with the minimum loss; 1f the contact is madeat point l, the rirst stepl of the potentiom eter (shown between thedelay circuit and the line amplifierl in line L2)"becomes eiiective.' ItContact isl made at point r2, the next. degree of loss is introduced inline L2, and so on; With the circuit connections shown'in thedrawingsvhowi If the con- A' n 15G cver,tlie control of these'fourrelays which'iuncvcaused to light. I

tion to adjust the received volume .is taken from the manually operatedswitch and is given to a group of automaticallyioperated relays-11, 12

and 13 corresponding to contact"rr1 2l, 22 and 23 corresponding tocontact 2, and 3l, 32 and 33 corresponding tor'contact 73.. Thisautomatic control functions Vto increase the receivedvoluine when thecharacteristics of the control circuit are such as tofcause llarnp Sito4 light and to decrease the received Yvolume when lamp S2 is Let it beassumed that the receiving loss introducedcin line'Lz is zero and thatlamp Sgfis lighted as a resultof. the operation of relays R and R.Acircuit may noW'be traced from ground over the` armature of'relay Re,the armal ture and upper contact of relay R', the armature and theWinding of relay R4, the ground being vof relay R and the left-,handarmature vof .relay Ri, over the vvindingotl relay 12 to battery `andground.I Relay llZ-.perates and this Operation causes the ,operation ofrelay 411,the leftfhand winding of'vvhich is connected in a circuitsimilar to that just traced. The closing ofthe lefthandcontact of relay11 (right-of the electrof magnet) completes` a locking circuit throughthe right-hand Winding, a back Contact oi relay 21 furnished over aswitch labeled "Automatic cutout key?, to be discussed hereinafter. Theclosing of the yright-lfiand Contact of relay 11 connects ground tothesecond relay associated with the receiving loss potentiometer,y andaccordingly step .1 of the potentiometer. becomes effective.

When, relays A12 rand 11 roperata-the operation of relay 13 is causedanda circuit is `clcsed through the contact o f rel,ay 13V andtheWinding of relay Ra` The operation of relay R5causes in turn theoperationV of, relay Re. `l The Winding ofY relay RJ. is included inthe`locking circuit ofrelay 1l. `Since this relay Rl; is,r'nade. slow-OpfVerating, it lvvillnot operate until relay Re has operated. The operationof relay Re removes ground from theoperatingcircuit of relay 12, causingthe release oiv that relay,but the delay in thefaction of .relay vRrisnot great enough to preventtheperation of `that relay while relay 12remains operated. The operation of relay R4 disconnects ground from-.thelzero relayvof the potentiometer andpermits relay; 12 to release, alsocausing the release of relay -13, vvhichisfollowed by the releaseofrelay R5v and the release of relay Ra, in turn.'` .The operation or".relayls' has permitted relays R and R to release. When relay R5releases, if-no further receiving loss should be introduced, relay Ralone will operate,

the, operation of relay R being prevented by the biasing Winding, and nofurther changewill be made in the received loss. If, however, additionalloss should be introduced, relay R as vvell Vas relayfRfWillagainoperate, and since'relay 11 is locked in its .operated position, groundWill Ynow be furnished over the left-hand armatures of` relays 12 and 11(leftof'vtheelectromagnets) to. relay 22. Relay 22 yoperates and isfollowed bythe operation of relays 2l, 23,"R5 and R6, this operationbeing similar to the operation of reflays .12., '11,' 13, R5 and Redescribed above. When relay21- operates, .it breaks the :locking circuitof relay 11,'ca`using the yrelease of that vrelay and thedisconnectionof ground from relayffl of vthepotentiometer. The release,4 of relays22,23, R5. and Reis brought about rby the release of relay 11. Shouldadditional loss bel-required, .re lays 32, 31 and `3 3 are operated inconjunction Awith relays R5 `and Rawith the required disgconnection volvtlr1 e l\1o. 2 potentiometer-relay c ground connection.

It Will be understood,v of

course, that while only three potentiometer steps are shown, anysuitablcnumber ymay be provided` S0 lay chains corresponding to bytheaddition ofthe necessary `resistances, control-relays and r 31, 32 and 33, forinstance.

Let itfbe assumed that potentiometer, and. that relay R releases,causing lamp Sito lightand thereby indicating that the receivinglossshould be decreased. It Will readily be understood that the ycircuitprovides in such aV `case rfor the'operationof relays 22,

21,23, R5. and Rs and the release of relay 31.

relay operated" with the resultant connectiorrfoi' step 3 ofthe 85 yInotherA Words, the circuit arrangement pro-V vides for the cutting outof loss in rsuitablesteps justas itprovides'fior. the connectinginofloss a insuitable steps. y l Y It; Will be noted that with theautomaticY cutout key at the right of relay'R4 inthe position operationof. relay R4, isr applied to certain ref.

under certain. conditions, Vto svvitch from .the v' automatic controlof'thereceived vo'lumetomanlual control of .that volumefWith-the circuitarrangementsshown, this shiftis made by simply throwingy theautomaticcutout .key .to the'o'p'po" site position, ground thusl beingconnectedto the.

arm of ,the .received-volume-oontrolswitch.` It4 f v'vvi1lbe`- noted,further, 'that'.this' switching" from 110 automatic to manual controlVdoesnotfalectthe operation oi'the signal lampsSriandS. These llampsstill 'function' to give the desired indicaf *tbn-S* i.;Asstated-hereinabove andasY shown in the drawings, the pad .associatedwith the .switchboard,.which, forethe' casevunder particular confsideratior'i, is a 6 decibel. padgfis,normallyvconnf'ectedinto,thecircuit. Itjhasbeen found from if v testsmade 'onthe transatlantic'circuit that with such Va pad the`collfdi'tion'sexisting are yapproiiij mately as tollovvs:

'Ifvgtheconnected circuit isa localcircuit4v orv af'tollt circuitequipped with four-vvirefechoVv suppressors, the receiving relayhangover time should be `.02..se'c'ond, and, sincethere is practicallyno differencebetvveen the Vretifirn losses jof those circuits, nosp'ecialchangefrom the normal is introduced in the iloss ahead 'of thereceiving amplierdetector or. the receiving loss; If' ashort toll line Y'Without echo Suppressors is connectedfto' the four--V Wire circuit,thereceiving relay hangover should be increased to .'05-se`cond,j,the,loss ahead ofthe receiving yampliiier-detector. is increasedby y4.5decibels, vsince the average' return loss is j now increased," by 12.5decibels." V,It the toll circuit about'"decibelsless andthe receivinglo'ssis I connected isa long' circuit, the receiving'relay 'rhangoverfshouldlbe increased to .1v second'the loss aheadfof thereceiving `amplifierld'etector is increasedby 9 decibels, the returnloss is! def creased by s decibels and' the reeeivingiqssj `is jincreasedby 17 decibels."

" To make adjustments Will be `ur'idersto'od fromV the discussion.contained n c tes-meeting above con-j ditions, the applicantsv providecertain circuit arfY rangements shown Yin Fig. 42. .The sleeve lead, it.L

hereinalcuve,I isfconnected to b'attery'when atoll connectio'n'is made;Such'va .connection'thus resuits in the operation of relayR,vvhichfdisconey nects thepad imrnediatelylto theA right ofvthat :6 iremy) Vfrom 'the circuit, redueirigfthe loss by e decibels, forinstance.` Likewise', batteryis con- Qnected 'to the winding" of relayR8, which operates andv adjusts Ythe loss introduced ahead of the'receiving sensitivity control, increases the hangover time'of thereceiving relay (see R3 ofFig. 1) Yfrom ..92 second to.05 second'andcuts out of the received-volume-control circuit the resistance r. Inadditiona receiving hangover adjustment key is provided'by which thevoperator mayj make further adjustment for the long toll circuitconnecition; j As indicated in the drawings,v he mayclose c the keyContact shownat the rightto place ground I von the Winding oi relay Re'and on the hangover controlV wire v-to the voice-operated relays, The

operationA of 'relay' R9 adjusts lthe loss' introduced` aheadj-V ci'theV sreceiving-sensitiVity-control, and theground connection on-thehangover control wire increasesthe hangover ltime of the receivingrelayiseefRc of VFig. V`1),loy Y.05 second; the opera-- tionof relay R'also-cuts outoithe rreceived-` volume-cntroldcircuit the resistanceV7.Y V'vIhe key contact at the left'can*be/opencdttorremove ground fromthewinding vof'relay Rrif noinerease oi liangover'time is desired, asinthe casezof they connection ofy a four-wireY circuit eduippedwthechosuppressors.

Tnene may. be connected tothe `four-.wire circuit'ajcircuit whichintroduces Vconditions slightly Vdifferent from Ythoseconsideredfahove"andfor which adjustment-is provided, as describedabove.' Nithsucha circuit connected, minor-adjustment shouid be -made inthe received volume. This adjustment' may be made `by the operation of'the control shown and labeledfReturn loss compensatorj It. will beunderstoodthat with Athe switch arm'in contactfwith. point 0s,`noiextraV resistance is connected into the controls, circuit; icontactjsmade at' point 1, an'extra'resisL ance oiflx ohms isgincludedrin thecontrolV circ'uit'; Vifcontac't is inade'at-point 2f,' a resistance of;6m ohms isa'ddedgjand so on, thev arrowf'indicating` the movement 0itheV switch arrii'ftoadjust ferihigherwreturn los's-Forthe purpose vofillusc Ytration,'a.resistance or" 3:1: ohms-is -added'rfor each'increase of 3 decibels in the return lossasA compared with the'case ofa typicalco'nnected circuit, -tha'sbee'n deemed desirablevto give a'some1-` what detailed Vdefscripti'on of the applicants inj `vvention inaspecific' form as applied toa cer-Y tain transmissionsystem, namely, atransoceanic radiotelephone system, for the purpose of;c'1earY Aillustrationfhn tliisform,1the' various VYcontrols other than the'control ofreceived volume are made"inanualljf,y forithe greater part,`and theseV variousmadjustments are'caused to control `jointlyandjautomaticallythe adjustment ofthe received volume. It will beunderstood, however, that the G" applicants invention-might'well beapplied to Aidely different circuits .and for the purposeY of obtainingvautomatic adjustment of acontrol other thanthat of the received volume.For, in-

" stancait is conceivable lthat it might be desirable to` causevariouscontrols of volume `.and sensi- 'f-transinitting volume fratherVthan Vthe received ,tivtyto'- join in the` automatic controlfofthevolume'. It vwill'loe clear'froman examination wire circuit having twopaths adapted` ior'transof FigL` 2 that rtheisimpies't of circuitchanges would lering ahout'suchga'result.' Accordingly,

it is'toV he understood Vthat the scope ofthe in-v Vventi'on is notlimited by thespecific disclosure y but is to he determined-by theappended claims,VV Y

what isjciainied is:Y n n Y Y, `1.y YIn a-transrnission system'inludinga four- Y2. 1n a two-way transmission mission in opposite directionsfandconnected in approximately conjugate relation and control apparatusresponsive to eurrents in said transmission paths, saidfour-wirecircuit'being adapted.- for connection toanyoneofdseveraltypesloi extend- -ing circuit introducing differentreturn charac- -terstics-,the method of transmission regulation whichconsists in adjusting'tii'e' operating', char'- acteristics of saidccntrolapparatus, adjusting the-'volume in one of r'said'transinission.pathsy causing the connection oi said four-wire'fcircuit'to -an extending circuit tol'intrcduce suitableA extras-'adjustment ofthe operating characteristics of said control apparatus,AV and causingleachfofv saidfadjustments to contribute directiy tothe the other ,ofsaid trans-r control of the volume'in mission paths.v

a four-wire circuit havingxtwo paths-,adapted for transmission inopposite directions and connectl edin approximately f conjugaterelation" andA switching devicesV responsive to currents'` in said'transmission paths and adapted for sustained y operation 'during 'Y ahangover period j of vrvariable y 100 l`ength,`"said four-Wire circuitbeing adapted `for connection to any one oiseveralftypesofextendsystemiinciuciiig ing circuit introducingdifierentw'returncharacteristics; `the f-method of transmission regulation whichlconsists in causing the connection lofran ved in approximately conjugaterelation.A and iconitrol apparatusresponsivef,`to currents in saidtransmission pathsfsaid-four-wire circuit being adapted forconnection-toanyone of-seveial'types of extending'circuit introducing' diiierentreturn characteristics, means for adjusting 'the'` volume in one 'ofsaid transmission pathsf'meansfor vad: justingY the sensitivities fofsaid control apparatus, means responsive!totheV connection of-saidYVfour-wire' circuit with-an extendingv circuit for adjusting theoperating characteristics'` of*A said control apparatus, and means forcontrolling the' volume inY ther other ofl'said transmission paths inaccordance Yv/iththe algebraic sumA of theefiects of.theoperationnofsaidseveral adjusting 'XneanSu Y Y' l; *1M f s' f i Y yY "34. Ina two-'Waytransmission"system including-a four-wire circuithaving` twopaths 'adapted for transmission in opposite ,directionsand'rcon-- nected` in approximately conjugate relation and-Y controlapparatus responsive to -currentsinfsaid'f transmission paths,l said1vfour-wire circuit .being l adaptedfor connectionto'varioustypes ofeX-Y tending circuit, means for'V adjustingthe loss at a lplurality ofpoints Iin thefour-wirefcircuitgrneans responsive totheconnectionvo-saidfour-'wire circuit 'With-ani eitendingfcircuit for adjusting thevoperating rcharacteristics of saidcontrolVv apparatus, 'andlmeans forcontrolling vthe; lossat another Apointv injthe jfour-wirecircuit?in`accordance'with the algebraic suin of.thc`e'iectsg of the operations ofsaid several-adjusting means. n i ,y

5. In a two-way-transmission circuit,A transinissionpaths 'adapted Vfortransmission in opposite' directions, circuit `control apparatusassociated withe'ach of said paths and responsive 5to,

ing on the aigebraicsum of the effects of the first mentionedoperations. Y f,

6. 1n a two-way transmission circuit, transl mission paths Aadapted fortransmission in opposite directions, circuit control apparatusassociated with each of said paths and responsive to currents therein,avpotentiometerassociated with each transmission path and apotentiometer as-y sociated .with each set of control apparatus, sev-veral switching means each designed` to adjust one of the potentiometers,a control circuit associated with one of said potentiometers, severalresistances each associated withione of said potentiometers and vadaptedto be varied simultaneously therewith, said variable Vresistancesandswitching means responsive to changesiin the series resistance ofsaid control, circuit for adjusting the potentiometerassociatedtherewithlv- '7. In a two-way transmission .'circuit,ltransmission paths adapted for transmissionin opbeing connectedin seriesin said control circuit,

posite' directionacircuit control apparatus associated with eachof saidpaths andrespon'si've to currents therein, a potentiometer associatedwith each transmission path and a potentiometerasf sociated with eachset of-controlapparatusy se'iv` eral switching means each designedto.adju'stone of the potentiometers, a` control,circuitassociy ated withoneof said potentiometers, several resistances each associated with oney ofLsaid po-v 'tentiometels and adapted to` .be yVaried [simul-` taneouslytherewith,'said variable resistances be" ing connected in series insaidcontrorcircuit,V and switching means responsive to changes be- Yyondpredeterminedvalues in the series resistance.

or" said control circuitfor adjusting the poten-j af tiometelassociatedtherewith. z i

SUMNER B; WRIGHT;

' EDMUNip R; TAYLOR.

